Абстрактные классы

PHP 5 поддерживает определение абстрактных классов и методов. Класс, который содержит по крайней мере один абстрактный метод, должен быть определен как абстрактный. Следует помнить, что нельзя создать экземпляр абстрактного класса. Методы, объявленные абстрактными, несут, по существу, лишь описательный смысл и не могут включать реализации.

При наследовании от абстрактного класса, все методы, помеченные абстрактными в родительском классе, должны быть определены в классе-потомке; кроме того, область видимости этих методов должна совпадать (или быть менее строгой). Например, если абстрактный метод объявлен как protected, то реализация этого метода должна быть либо protected либо public, но никак не private. Более того, сигнатуры методов должны совпадать, т.е. контроль типов (type hint) и количество обязательных аргументов должно быть одинаковым. К примеру, если в дочернем классе указан необязательный параметр, которого нет в сигнатуре абстрактного класса, то в данном случае конфликта сигнатур не будет. Это правило также применяется к конструкторам начиная с версии PHP 5.4, ранее сигнатуры конструкторов могли отличаться.

Пример #1 Пример абстрактного класса

<?php
abstract class AbstractClass
{
   
/* Данный метод должен быть определён в дочернем классе */
    
abstract protected function getValue();
    abstract protected function 
prefixValue($prefix);

   
/* Общий метод */
    
public function printOut() {
        print 
$this->getValue() . "\n";
    }
}

class 
ConcreteClass1 extends AbstractClass
{
    protected function 
getValue() {
        return 
"ConcreteClass1";
    }

    public function 
prefixValue($prefix) {
        return 
"{$prefix}ConcreteClass1";
    }
}

class 
ConcreteClass2 extends AbstractClass
{
    public function 
getValue() {
        return 
"ConcreteClass2";
    }

    public function 
prefixValue($prefix) {
        return 
"{$prefix}ConcreteClass2";
    }
}

$class1 = new ConcreteClass1;
$class1->printOut();
echo 
$class1->prefixValue('FOO_') ."\n";

$class2 = new ConcreteClass2;
$class2->printOut();
echo 
$class2->prefixValue('FOO_') ."\n";
?>

Результат выполнения данного примера:

ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2

Пример #2 Пример абстрактного класса

<?php
abstract class AbstractClass
{
    
// Наш абстрактный метод должен определять только необходимые аргументы
    
abstract protected function prefixName($name);

}

class 
ConcreteClass extends AbstractClass
{

    
// Наш дочерний класс может также определять необязательные аргументы, не указанные в сигнатуре родительского метода
    
public function prefixName($name$separator ".") {
        if (
$name == "Pacman") {
            
$prefix "Mr";
        } elseif (
$name == "Pacwoman") {
            
$prefix "Mrs";
        } else {
            
$prefix "";
        }
        return 
"{$prefix}{$separator} {$name}";
    }
}

$class = new ConcreteClass;
echo 
$class->prefixName("Pacman"), "\n";
echo 
$class->prefixName("Pacwoman"), "\n";
?>

Результат выполнения данного примера:

Mr. Pacman
Mrs. Pacwoman

Код, предназначенный для прежних версий PHP, должен работать без изменений, если в нём отсутствуют классы или функции, именованные 'abstract'.

Коментарии

Автор:
I don't agree with jfkallens' last comparison between Abstract Classes & Object Interfaces completely.

In an Abstract Class, you can define how some methods work, where as in an Object Interface you can not.

An Object Interface is essentually nothing but a list of function names that a class must define if the class implements that interface.

An Abstract Class is essentually a prototype which hints towards what extending classes should be doing.
An Abstract Class can also be thought of as a Base Class that provides some basic functionality, & also defines a built-in Object Interface that all extending classes will implement.

So, an Object Interface is really a built-in part of an Abstract Class.
2007-06-24 07:09:17
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Ok...the docs are a bit vague when it comes to an abstract class extending another abstract class.  An abstract class that extends another abstract class doesn't need to define the abstract methods from the parent class.  In other words, this causes an error:

<?php
abstract class class1 {
  abstract public function 
someFunc();
}
abstract class 
class2 extends class1 {
  abstract public function 
someFunc();
}
?>

Error: Fatal error: Can't inherit abstract function class1::someFunc() (previously declared abstract in class2) in /home/sneakyimp/public/chump.php on line 7

However this does not:

<?php
abstract class class1 {
  abstract public function 
someFunc();
}
abstract class 
class2 extends class1 {
}
?>

An abstract class that extends an abstract class can pass the buck to its child classes when it comes to implementing the abstract methods of its parent abstract class.
2007-10-09 20:05:57
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Just one more time, in the simplest terms possible:

An Interface is like a protocol. It doesn't designate the behavior of the object; it designates how your code tells that object to act. An interface would be like the English Language: defining an interface defines how your code communicates with any object implementing that interface.

An interface is always an agreement or a promise. When a class says "I implement interface Y", it is saying "I promise to have the same public methods that any object with interface Y has".

On the other hand, an Abstract Class is like a partially built class. It is much like a document with blanks to fill in. It might be using English, but that isn't as important as the fact that some of the document is already written.

An abstract class is the foundation for another object. When a class says "I extend abstract class Y", it is saying "I use some methods or properties already defined in this other class named Y".

So, consider the following PHP:
<?php
class implements { } // this is saying that "X" agrees to speak language "Y" with your code.

class extends { } // this is saying that "X" is going to complete the partial class "Y".
?>

You would have your class implement a particular interface if you were distributing a class to be used by other people. The interface is an agreement to have a specific set of public methods for your class.

You would have your class extend an abstract class if you (or someone else) wrote a class that already had some methods written that you want to use in your new class.

These concepts, while easy to confuse, are specifically different and distinct. For all intents and purposes, if you're the only user of any of your classes, you don't need to implement interfaces.
2008-03-27 15:56:30
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Автор:
here is a real world example of abstract using:

a (abstract) person class
a student and an employee final class, which extends person class.

simple theory is that both student and employee is an extension of the person class.  the difference lies on which table the data is written on, and what other pre processing (ie mandatory field checking, type checking, etc.) needed before writing each of the classes.

codes:

<?php

abstract class person {
   
    abstract protected function 
write_info();
   
    public 
$LastName;
    public 
$FirstName;
    public 
$BirthDate;
   
    public function 
get_Age($today=NULL){
       
//age computation function
   
}
}

final class 
employee extends person{
    public 
$EmployeeNumber;
    public 
$DateHired;

    public function 
write_info(){
        echo 
"Writing "$this->LastName "'s info to emloyee dbase table";   
       
//ADD unique mandatory checking unique to EMPLOYEE ONLY
        //actual sql codes here
   
}
}

final class 
student extends person{
    public 
$StudentNumber;
    public 
$CourseName;
   
    public function 
write_info(){
        echo 
"Writing "$this->LastName "'s info to student dbase table";
       
//ADD unique mandatory checking unique to STUDENT ONLY
        //actual sql codes here
   
}
}

///----------
$personA = new employee;
$personB = new student;

$personA->FirstName="Joe";
$personA->LastName="Sbody";

$personB->FirstName="Ben";
$personB->LastName="Dover";

$personA->write_info();
?>

OUTPUT:Writing Sbody's info to emloyee dbase table
2008-06-03 00:04:28
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Автор:
There isn't really that much of a great hurdle in understanding these things, there really isn't. 

If you're defining a new class that is abstract, it means that you can make some non-abstract functions that you can use to define the general underlying behavior of that class along side abstract ones. 

In interfaces, you can't do that since functions defined therewithin cannot have a body.

Abstract functions you use for classes that must define more specific behavior when "extending" your class. 

So for a crude example - define by your non-abstract functions how that particular object (which may be part of a larger class hierarchy) would store and process it's data in SQL, XML, etc.

Then define abstract functions which allow someone implementing that class to specifically manipulate the data that is to be stored. Then require a format which this data must be returned in, and then in your non-abstract functions call those functions on destruction, in normal runtime, and so on. 

Again, non-abstract functions, or even another class could implement the finer points of ensuring that data is in the correct format, and so on, ad infinitum. 

It isn't too much of a reach to say that if you used a normal class instead of an abstract class, then there isn't much intrinsic requirement between the two classes. 

Assuming that you wanted the functions to use each-others functions and you'd need to use them specifically by name, you'd have to write some code which checked to see -- lamely using function_exists() and other lamery -- if that class has the function you require for interoperability, when you could avoid all possible confusion and headaches by simply using the right tool for the job.

And reading a decent OOP book.
2009-09-22 19:13:37
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
One fairly important difference between php's abstract functions and, say, Java, is that php does not specify the return type in any way - or indeed whether there has to be one.

<?php public abstract function square($number); ?>

could be implemented by...

<?php
public function square($number) {
   return 
$number*$number;
}
?>

or 

<?php
public function square($number) {
   print (
$number*$number);
}
?>

So you need to take care that incompatibilities don't arise due to not returning the right kind of value and this is not enforced in any way.
2009-10-13 05:49:34
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
"additionally, these methods must be defined with the same (or a less restricted) visibility."

The words were not restricted in abstract class but also normal classes,
the method in child Class which overwrites the parent Class can also change the the visibility of the method to same or less restricted.
for example:
<?php
class ClassOne {
    protected static 
$staticone 'nathan';
    protected function 
changestaticone() {
        return 
self::$staticone 'john';
    }
}

class 
ClassTwo extends ClassOne {
    public function 
changestaticone() {
        return 
self::$staticone 'Alexey';
    }

$classtwo = new ClassTwo();
echo 
$classtwo->changestaticone();
2009-11-17 00:55:50
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Here's an example that helped me with understanding abstract classes. It's just a very simple way of explaining it (in my opinion). Lets say we have the following code:

<?php
class Fruit {
    private 
$color;
   
    public function 
eat() {
       
//chew
   
}
   
    public function 
setColor($c) {
       
$this->color $c;
    }
}

class 
Apple extends Fruit {
    public function 
eat() {
       
//chew until core
   
}
}

class 
Orange extends Fruit {
    public function 
eat() {
       
//peel
        //chew
   
}
}
?>

Now I give you an apple and you eat it.

<?php
$apple 
= new Apple();
$apple->eat();
?>

What does it taste like? It tastes like an apple. Now I give you a fruit.

<?php
$fruit 
= new Fruit();
$fruit->eat();
?>

What does that taste like??? Well, it doesn't make much sense, so you shouldn't be able to do that. This is accomplished by making the Fruit class abstract as well as the eat method inside of it.

<?php
abstract class Fruit {
    private 
$color;
   
    abstract public function 
eat();
   
    public function 
setColor($c) {
       
$this->color $c;
    }
}
?>

Now just think about a Database class where MySQL and PostgreSQL extend it. Also, a note. An abstract class is just like an interface, but you can define methods in an abstract class whereas in an interface they are all abstract.
2010-01-01 01:59:14
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Автор:
Incidentally, abstract classes do not need to be base classes:

<?php
class Foo {
    public function 
sneeze() { echo 'achoooo'; }
}

abstract class 
Bar extends Foo {
    public abstract function 
hiccup();
}

class 
Baz extends Bar {
    public function 
hiccup() { echo 'hiccup!'; }
}

$baz = new Baz();
$baz->sneeze();
$baz->hiccup();
?>
2010-07-28 13:36:02
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Please be aware of the visibility of the parent fields. If the fields are private, then you are not going to see those fields in their childrens. Its basic OOP, but can be problematic sometimes.
2010-12-26 08:29:22
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Abstraction and interfaces are two very different tools. The are as close as hammers and drills. Abstract classes may have implemented methods, whereas interfaces have no implementation in themselves.

Abstract classes that declare all their methods as abstract are not interfaces with different names. One can implement multiple interfaces, but not extend multiple classes (or abstract classes).

The use of abstraction vs interfaces is problem specific and the choice is made during the design of software, not its implementation. In the same project you may as well offer an interface and a base (probably abstract) class as a reference that implements the interface. Why would you do that?

Let us assume that we want to build a system that calls different services, which in turn have actions. Normally, we could offer a method called execute that accepts the name of the action as a parameter and executes the action.

We want to make sure that classes can actually define their own ways of executing actions. So we create an interface IService that has the execute method. Well, in most of your cases, you will be copying and pasting the exact same code for execute.

We can create a reference implemention for a class named Service and implement the execute method. So, no more copying and pasting for your other classes! But what if you want to extend MySLLi?? You can implement the interface (copy-paste probably), and there you are, again with a service. Abstraction can be included in the class for initialisation code, which cannot be predefined for every class that you will write.

Hope this is not too mind-boggling and helps someone. Cheers,
Alexios Tsiaparas
2011-03-26 17:57:02
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Автор:
The documentation says: "It is not allowed to create an instance of a class that has been defined as abstract.". It only means you cannot initialize an object from an abstract class. Invoking static method of abstract class is still feasible. For example:
<?php
abstract class Foo
{
    static function 
bar()
    {
        echo 
"test\n";
    }
}

Foo::bar();
?>
2011-05-31 22:27:48
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Abstract classes may have an final constructor, and sometime it makes sense to implement a class with a final constructor.

<?php
abstract class AbstractModel
{
   
//our models must use the default constuctor
       
public final function __construct(){}
    public function 
inject($array){
        foreach(
array_keys(get_class_vars(get_called_class()))  as $property){
           
$this->$property $array[$property];
        }
    }
}

class 
ProductModel extends AbstractModel
{
    public 
$name;
    public 
$price;
    protected 
$id;
   
    public function 
getId(){return $this->id;}
}

class 
Factory{
    private 
$dataSource;
    public function 
__consruct($dataSource){
       
$this->dataSource $dataSource;
    }
   
    public function 
get($class$table$filter$orderby$limit){
       
$result = array();
        foreach(
$datasource->fetchAssoc($table$filter$orderby$limit) as $rawData){
           
$obj = new $class();//this can only work if ALL models have a default constructor
           
$obj->inject($rawData);
           
$result[] = $obj;
        }
        return 
$result;
    }
}
?>

Note: This is a very simple example, and I am aware that there are other (better) ways to do this.
Oliver Anan
2011-11-27 10:07:25
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Invoking static method of abstract class should be removed.

What interfaces are?
- A mean to ensure all implementation have the same methods implemented.

What is an abstract class?
- It is a interface that can also include some concrete methods.

Is it right for the developer to be able to invoke a static method of an interface?
- I think not.

The GoF teach us to rely on abstract classes and interfaces to hide differences between subclasses from clients.
- Interface defines an object’s use (protocol)
- Implementation defines particular policy

I don't think one should be able to call some abstract logic that is defined inside an abstract class, without even inheriting the class itself.
2014-02-10 20:33:25
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Please note order or positioning of the classes in your code can affect the interpreter and can cause a Fatal error: Class 'YourClass' not found if there are multiple levels of abstraction out of order.  For example:
<?php
abstract class horse extends animal {
    public function 
get_breed() { return "Jersey"; }
}

class 
cart extends horse {
    public function 
get_breed() { return "Wood"; }
}
 
abstract class 
animal {
    public abstract function 
get_breed();
}

$cart = new cart();
print(
$cart->get_breed());
?>

this outputs:
Wood

However, if you put the cart before the abstract horse (literally):

<?php
class cart extends horse {
    public function 
get_breed() { return "Wood"; }
}

abstract class 
horse extends animal {
    public function 
get_breed() { return "Jersey"; }
}
 
abstract class 
animal {
    public abstract function 
get_breed();
}

$cart = new cart();
print(
$cart->get_breed());
?>

this throws an error:
Fatal error: Class 'horse' not found

So, when using multiple levels of abstraction, be careful of the positioning of the classes within the source code - and don't put the cart before the abstract horse.
2014-09-11 18:43:52
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Just in case you are confused about function arguments: 

/*************Example 1********************/

abstract class my_class {
     abstract public function my_function($number);
}

class subclass extends my_class {
     public function my_function($new_number, $string = ' is an integer!!!')
     {
          echo $new_number . $string;
     }
}
$var = new subclass();
$var->my_function(1024); //this will output: 1024 is an integer!!!

/*************Example 2********************/
abstract class my_class {
     abstract public function my_function($number);
}

class subclass extends my_class {
    //now $string = ' is a float!!!'
     public function my_function($new_number, $string = ' is a float!!!')
     {
          echo $new_number . $string;
     }

}
$var = new subclass();
//added ' is an integer'
$var->my_function(1024, ' is an integer!!!'); //this will output: 1024 is an integer!!!, rewrote $string.

/*************Example 3********************/

abstract class my_class {
     abstract public function my_function($number);
}

class subclass extends my_class {
     //now $string isn't initialized
     public function my_function($new_number, $string )
     {
          echo $new_number . $string;
     }

}

$var = new subclass();
$var->my_function(1024, ' is an integer!!!'); /*this will trigger a fatal error of incompatibility between subclass::my_function() and my_class::my_function($number)*/

/*************Example 4********************/

abstract class my_class {
     abstract public function my_function($number);
}

class subclass extends my_class {   
     public function my_function($new_number, $string )
     {
          echo $new_number . $string;
     }

}
$var = new subclass();
//no second argument, no matter
$var->my_function(1024);//fatal error  too. Optional arguments have to be initialized in the extending class function.
2014-09-25 12:33:12
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
You can use an abstract class like this too:

abstract class A{
    public function show(){
        echo 'A';
    }
}
class B extends A{
    public function hello(){
        echo 'B';
        parent::show();
    }
}

$obj = new B;
$obj->hello(); // BA
# See that the abstract class does not have at least one abstract method
# Even in this case, I'm still able to extend it, or call its non-abstract member
2015-04-08 11:10:52
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
The self keyword in an abstract class will refer to the abstract class itself, not the extending class no matter what.

For instance the following code looks really pretty, yet results in a Fatal error (Cannot instantiate abstract class Basic).

<?php
abstract class Basic {
    public static function 
doWork() {
        return (new 
self())->work();
    }

    abstract protected function 
work();
}

class 
Keeks extends Basic {
    protected function 
work() {
        return 
'Keeks';
    }
}

echo 
Keeks::doWork();
?>
2015-09-26 18:26:46
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Автор:
The abstract keyword cannot be used to dictate properties or class constants that a derivative class must set/define. Instead, those required properties or constants can be included in the abstract class with the expectation that they will be overridden in derivative classes, which at least ensures that the desired property/constant is set/defined.
2016-01-24 21:03:30
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
Автор:
I've found an inconsistency with: Example #2 Abstract class example

If you remove the default value of $separator

<?php
   
public function prefixName($name$separator) {
       
// ...
   
}
?>

Then php will show this fatal message: 
Fatal error: Declaration of ConcreteClass::prefixName() must be compatible with AbstractClass::prefixName($name) in /index.php on line 23

Stange enough it gives an incorrect declaration of "ConcreteClass::prefixName()"... It is missing both arguments. Because of that I'm assuming that this is just a bug that maybe already has been taking care of in newer versions. (Or is just specific to my version) I'm mainly noting this because it was driving me absolutely insane in some test code that I was writing derived from Example #2 (without a default value for an extra argument). Perhaps this saves some frustrations to other people.

--
Please note that i'm running this on php5.5. 
OS: ubuntu-16.04-server-amd64.iso
Repo: ppa:ondrej/php

# php5.5 --version
PHP 5.5.36-2+donate.sury.org~xenial+1 (cli)
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2016-05-29 16:26:44
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
A snippet of code to help you understand a bit more about properties inside abstract classes:
<?php
abstract class anotherAbsClass
{
   
// Define and set a static property
   
static $stProp 'qwerty';        // We can still use it directly by the static way
    // Define and set a protected property
   
protected $prProp 'walrus';
   
// It is useless to set any other level of visibility for non-static variables of an abstract class.
    // We cannot access to a private property even inside a declared method of an abstract class because we cannot call that method in the object context.
    // Implementation of a common method
   
protected function callMe() {
        echo 
'On call: ' $this->prProp PHP_EOL;
    }
   
// Declaration of some abstract methods
   
abstract protected function abc($arg1$arg2);
    abstract public function 
getJunk($arg1$arg2$arg3$junkCollector true);   
   
// Note: we cannot omit an optional value without getting error if it has already been declared by an abstract class
}

class 
someChildClass extends anotherAbsClass
{   
    function 
__construct() {
        echo 
$this->callMe() . PHP_EOL;    // now we get the protected property $prProp inhereted from within the abstract class
   
}
   
// There must be implementation of the declared functions abc and getJunk below
   
protected function abc($val1$val) {
       
// do something
   
}
    function 
getJunk($val1$val2$val3$b false) {    // optional value is neccessary, because it has been declared above
        // do something
   
}
}

echo 
anotherAbsClass::$stProp;    // qwerty
$objTest = new someChildClass;   // On call: walrus 
?>
2016-10-12 16:46:39
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
An interface specifies what methods a class must implement, so that anything using that class that expects it to adhere to that interface will work.

eg: I expect any $database to have ->doQuery(), so any class I assign to the database interface should implement the databaseInterface interface which forces implementation of a doQuery method.

<?php
interface dbInterface {
    public function 
doQuery();
}

class 
myDB implements dbInterface {
    public function 
doQuery() {
     
/* implementation details here */
   
}
}

$myDBObj = new myDB()->doQuery();
?>

An abstract class is similar except that some methods can be predefined. Ones listed as abstract will have to be defined as if the abstract class were an interface.

eg. I expect my $person to be able to ->doWalk(), most people walk fine with two feet, but some people have to hop along :(

<?php
interface PersonInterface() {
   
/* every person should walk, or attempt to */
   
public function doWalk($place);
   
/* every person should be able to age */
   
public function doAge();
}

abstract class 
AveragePerson implements PersonInterface() {
    private 
$_age 0;
    public function 
doAge() {
       
$this->_age $this->_age+1;
    }
    public function 
doWalk($place) {
        echo 
"I am going to walk to $place".PHP_EOL;
    }
   
/* every person talks differently! */
   
abstract function talk($say);
}

class 
Joe extends AveragePerson {
    public function 
talk($say) {
       echo 
"In an Austrailian accent, Joe says: $say".PHP_EOL;
    }
}

class 
Bob extends AveragePerson {
    public function 
talk($say) {
        echo 
"In a Canadian accent, Bob says: $say".PHP_EOL;
    }
    public function 
doWalk($place) {
        echo 
"Bob only has one leg and has to hop to $place".PHP_EOL;
    }
}

$people[] = new Bob();
$people[] = new Joe();

foreach (
$people as $person) {
   
$person->doWalk('over there');
   
$person->talk('PHP rules');
}
?>
2017-03-02 07:36:36
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html
This example will hopefully help you see how abstract works, how interfaces work, and how they can work together. This example will also work/compile on PHP7, the others were typed live in the form and may work but the last one was made/tested for real:

<?php

const ¶ PHP_EOL;

// Define things a product *has* to be able to do (has to implement)
interface productInterface {
    public function 
doSell();
    public function 
doBuy();
}

// Define our default abstraction
abstract class defaultProductAbstraction implements productInterface {
    private 
$_bought false;
    private 
$_sold false;
    abstract public function 
doMore();
    public function 
doSell() {
       
/* the default implementation */
       
$this->_sold true;
        echo 
"defaultProductAbstraction doSell: {$this->_sold}".;
    }
    public function 
doBuy() {
       
$this->_bought true;
        echo 
"defaultProductAbstraction doBuy: {$this->_bought}".;
    }
}

class 
defaultProductImplementation extends defaultProductAbstraction {
    public function 
doMore() {
        echo 
"defaultProductImplementation doMore()".;
    }
}

class 
myProductImplementation extends defaultProductAbstraction {
    public function 
doMore() {
        echo 
"myProductImplementation doMore() does more!".;
    }
    public function 
doBuy() {
        echo 
"myProductImplementation's doBuy() and also my parent's dubai()".;
       
parent::doBuy();
    }
}

class 
myProduct extends defaultProductImplementation {
    private 
$_bought=true;
    public function 
__construct() {
       
var_dump($this->_bought);
    }
    public function 
doBuy () {
       
/* non-default doBuy implementation */
       
$this->_bought true;
        echo 
"myProduct overrides the defaultProductImplementation's doBuy() here {$this->_bought}".;
    }
}

class 
myOtherProduct extends myProductImplementation {
    public function 
doBuy() {
        echo 
"myOtherProduct overrides myProductImplementations doBuy() here but still calls parent too".;
       
parent::doBuy();
    }
}

echo 
"new myProduct()".;
$product = new myProduct();

$product->doBuy();
$product->doSell();
$product->doMore();

echo 
."new defaultProductImplementation()".;

$newProduct = new defaultProductImplementation();
$newProduct->doBuy();
$newProduct->doSell();
$newProduct->doMore();

echo 
."new myProductImplementation".;
$lastProduct = new myProductImplementation();
$lastProduct->doBuy();
$lastProduct->doSell();
$lastProduct->doMore();

echo 
."new myOtherProduct".;
$anotherNewProduct = new myOtherProduct();
$anotherNewProduct->doBuy();
$anotherNewProduct->doSell();
$anotherNewProduct->doMore();
?>

Will result in:
<?php
/*
new myProduct()
bool(true)
myProduct overrides the defaultProductImplementation's doBuy() here 1
defaultProductAbstraction doSell: 1
defaultProductImplementation doMore()

new defaultProductImplementation()
defaultProductAbstraction doBuy: 1
defaultProductAbstraction doSell: 1
defaultProductImplementation doMore()

new myProductImplementation
myProductImplementation's doBuy() and also my parent's dubai()
defaultProductAbstraction doBuy: 1
defaultProductAbstraction doSell: 1
myProductImplementation doMore() does more!

new myOtherProduct
myOtherProduct overrides myProductImplementations doBuy() here but still calls parent too
myProductImplementation's doBuy() and also my parent's dubai()
defaultProductAbstraction doBuy: 1
defaultProductAbstraction doSell: 1
myProductImplementation doMore() does more!

*/
?>
2017-03-02 07:36:57
http://php5.kiev.ua/manual/ru/language.oop5.abstract.html

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